Refrigerator

ABSTRACT

There is disclosed a refrigerator in which a refrigerant circuit on a high-pressure side is operated in a supercritical state, and an object of the refrigerator is to improve a freezing capacity while securely preventing dew condensation at an opening edge by a condenser. In the refrigerator including the refrigerant circuit constituted of a compressor, the condenser, a throttle means and an evaporator; and a dew condensation preventive pipe constituting a part of the condenser and disposed along the opening edge of an insulation box member, the refrigerant circuit on the high-pressure side is operated in the supercritical state, and the dew condensation preventive pipe is positioned on an upstream side of a refrigerant downstream region of the condenser.

BACKGROUND OF THE INVENTION

The present invention relates to a refrigerator in which a dewcondensation preventive pipe constituting a part of a condenser (or gascooler or condensing heat exchanger or gas cooling heat exchanger) of arefrigerant circuit is disposed along an opening edge of an insulationbox member in order to prevent dew condensation of a main body. Thepresent invention more particularly relates to a refrigerator in which arefrigerant circuit on a high-pressure side is operated in asupercritical state.

Heretofore, in this type of refrigerator, an insulation box member isconstituted of a metallic outer box, an inner box made of a hardsynthetic resin and an insulation material foamed and filled betweenboth the boxes. In the inner box, a freezing chamber and a refrigeratingchamber are constituted so as to freeze or refrigerate and store foodand the like in the inner box. An insulation door is disposed on a frontsurface of this insulation box member, and the freezing andrefrigerating chambers are openably closed by the insulation door.Moreover, a mechanical chamber in which a compressor and the like are tobe installed is constituted in a lower part of the insulation boxmember.

Furthermore, when the compressor is operated, a refrigerant is suckedinto the compressor and compressed to constitute a high-temperaturehigh-pressure gas, and the gas enters a condenser. While the refrigerantflows through the condenser, heat exchange between the refrigerant andambient air is performed. The refrigerant rejects (or transfers) heatand is condensed. After a pressure of the refrigerant which hascondensed in the condenser is reduced by a throttle means, therefrigerant enters an evaporator and evaporates. At this time, therefrigerant absorbs the heat from a surrounding to exhibit a coolingfunction. The air subjected to the heat exchange between the air and therefrigerant and cooled in the evaporator is circulated through chamberssuch as the freezing chamber and the refrigerating chamber by blowingmeans such as a fan to cool objects stored in the chambers.

In such a refrigerator, when the heat leaks from a portion between theinsulation box member and the insulation door, a surface temperature inthe vicinity of this portion drops below a temperature (outside airtemperature) around a position where the refrigerator is installed, andthe temperature is not more than a dew point. In this case, adisadvantage occurs that a moisture in the air is attached, that is,so-called dew condensation is generated. Therefore, a heater isinstalled in a portion of the refrigerator in which the dew condensationis easily generated to thereby heat the portion. In consequence, thegeneration of the dew condensation in such a portion has been prevented.

However, a disadvantage occurs that a cooling performance deterioratesor power consumption increases owing to the heat of the heater. To solvesuch a problem, a refrigerant downstream region of the condenser of therefrigerant circuit is disposed in the portion in which the dewcondensation is easily generated. The portion is thus heated to therebyprevent the generation of the dew condensation. Specifically, forexample, a pipe constituting the refrigerant downstream region of thecondenser of the refrigerator is disposed along an opening edge of theinsulation box member, that is, the refrigerant pipe of the refrigerantdownstream region of the condenser is used as the dew condensationpreventive pipe. In consequence, a high-temperature high-pressurerefrigerant gas compressed by the compressor is allowed to condense inthe condenser. The refrigerant condenses at a constant temperature (apredetermined condensation temperature without any temperature change).Therefore, the opening edge can be heated by the heat of the refrigerantpassed through the condenser (including a dew condensation preventivepipe) to prevent such dew condensation (see, e.g., Japanese PatentApplication Laid-Open Nos. 7-239178, 10-197122).

In addition, in recent years, such a refrigerator cannot use aheretofore used chlorofluorocarbon-based refrigerant owing to a problemof global environment destruction. Therefore, an attempt to use carbondioxide (CO₂) which is a natural refrigerant as a substitute for thechlorofluorocarbon-based refrigerant.

When the carbon dioxide refrigerant is compressed, the refrigerantcircuit on the high-pressure side is sometimes brought into asupercritical state. When the refrigerant circuit on the high-pressureside is brought into the supercritical state in this manner, therefrigerant does not condense in the condenser, and rejects the heatwhile maintaining the supercritical state. Therefore, the temperature ofthe refrigerant drops owing to the hat rejection. To solve this problem,a refrigerant temperature at an outlet of the dew condensationpreventive pipe in the refrigerant downstream region of the condenserneeds to be maintained at a value sufficient for preventing the dewcondensation along the opening edge. That is, the refrigeranttemperature at an outlet of the condenser has to be maintained at atemperature which is not less than the dew point so that the dewcondensation is not generated. Therefore, the refrigerant temperature atthe outlet of the condenser cannot be lowered to a value sufficient forsecuring a freezing capability, and specific enthalpy of the refrigerantflowing through the evaporator also increases. In consequence, a problemhas occurred that the freezing capability of the evaporator remarkablydeteriorates, and the cooling in the freezing chamber and therefrigerating chamber is obstructed.

SUMMARY OF THE INVENTION

The present invention has been developed to solve the problem of such aconventional technology, and an object is to improve a freezingcapability while securely preventing dew condensation along an openingedge by a condenser in a refrigerator in which a refrigerant circuit ona high-pressure side is operated in a supercritical state.

This is, a refrigerator of a first invention comprises: a refrigerantcircuit constituted of a compressor, a condenser, a throttle means andan evaporator and operated on a high-pressure side in a supercriticalstate; and a dew condensation preventive pipe constituting a part of thecondenser and disposed along an opening edge of an insulation boxmember. The refrigerator is characterized in that the condenser includesat least a first condenser and a second condenser and that the dewcondensation preventive pipe is positioned between the first condenserand the second condenser.

A second invention is characterized in that the above invention furthercomprises: a bypass pipe connected in parallel with the dew condensationpreventive pipe; and a channel control unit which controls whether topass a refrigerant through the dew condensation preventive pipe or thebypass pipe.

According to a third invention, the above inventions are characterizedin that carbon dioxide is used as the refrigerant of the refrigerantcircuit.

According to the first invention, in the refrigerator comprising: therefrigerant circuit constituted of the compressor, the condenser, thethrottle means and the evaporator and operated on the high-pressure sidein the supercritical state; and the dew condensation preventive pipeconstituting a part of the condenser and disposed along the opening edgeof the insulation box member, the condenser includes at least the firstcondenser and the second condenser, and the dew condensation preventivepipe is positioned between the first condenser and the second condenser.Therefore, while a temperature at an outlet of the dew condensationpreventive pipe is set to a value sufficient for preventing dewcondensation along the opening edge, a temperature of the refrigerant ina refrigerant downstream region can sufficiently be lowered.

In consequence, a refrigerant temperature at an outlet of the condensercan be lowered to a value sufficient for securing a freezing capacity.While the dew condensation along the opening edge is prevented, thefreezing capacity can be improved.

Moreover, in the present invention, since the dew condensationpreventive pipe is disposed between the first condenser and the secondcondenser, a temperature of the dew condensation preventive pipesometimes rises more than necessary during pull-down or the like.However, in a case where the refrigerator further comprises: the bypasspipe connected in parallel with the dew condensation preventive pipe;and the channel control unit which controls whether to pass therefrigerant through the dew condensation preventive pipe or the bypasspipe as in the second invention, when the temperature of the dewcondensation preventive pipe rises more than necessary, the refrigerantcan be passed through the bypass pipe to prevent an excessivetemperature rise of the dew condensation preventive pipe.

In consequence, a disadvantage can be avoided in advance that owing tothe excessive temperature rise of the dew condensation preventive pipe,a feeling of discomfort is given to a user or the user gets burnt whentouching the pipe. Moreover, safety can be secured.

Especially, according to the present invention, carbon dioxide can beused as the refrigerant of the refrigerator as in the third invention.This also contributes to solution of an environmental problem.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a refrigerant circuit diagram of a refrigerator according toone embodiment of the present invention;

FIG. 2 is a schematic diagram schematically showing a refrigerantcircuit of the refrigerator of FIG. 1;

FIG. 3 is the Mollier diagram of the refrigerator of the presentembodiment;

FIG. 4 is a refrigerant circuit diagram of a refrigerator according toanother embodiment of the present invention;

FIG. 5 is the Mollier diagram of the refrigerator of FIG. 5;

FIG. 6 is a refrigerant circuit diagram of a refrigerator according tostill another embodiment of the present invention;

FIG. 7 is a refrigerant circuit diagram of a conventional refrigerator;

FIG. 8 is a schematic diagram schematically showing a refrigerantcircuit of the refrigerator of FIG. 7;

FIG. 9 is the Mollier diagram of the refrigerator of FIG. 7 in a casewhere a conventional refrigerant is used (in a case where asupercritical pressure is not achieved in a refrigerant circuit on ahigh-pressure side); and

FIG. 10 is the Mollier diagram of the refrigerator of FIG. 7 in a casewhere a refrigerant circuit on a high-pressure side is operated in asupercritical state.

DESCRIPTION OF THE PREFERABLE EMBODIMENTS

The present invention is directed to a refrigerator in which arefrigerant circuit on a high-pressure side is operated in asupercritical state and in which a dew condensation preventive pipeconstituting a part of a condenser is disposed along an opening edge ofan insulation box member to prevent dew condensation along the openingedge. The present invention has been developed to eliminate adisadvantage that specific enthalpy of a refrigerant flowing through anevaporator increases and a freezing capacity deteriorates in a casewhere a temperature of the refrigerant flowing through the dewcondensation preventive pipe is maintained at a value sufficient forpreventing dew condensation along the opening edge. An object to improvethe freezing capacity while securely preventing dew condensation alongthe opening edge of the refrigerator is realized by positioning the dewcondensation preventive pipe constituting a part of the condenserbetween a first condenser and a second condenser. Embodiments of thepresent invention will hereinafter be described with reference to thedrawings.

Embodiment 1

FIG. 1 shows a refrigerant circuit diagram of a refrigerator accordingto one embodiment of the present invention, and FIG. 2 shows a schematicdiagram of a dew condensation preventive pipe disposed along an openingedge of an insulation box member of the refrigerator, respectively. Amain body of a refrigerator 1 of the embodiment is constituted of anouter box 2 having a front opening and formed of a steel plate; an innerbox 3 made of a thin hard synthetic resin (e.g., an ABS resin); aninsulation box member 4 made of foamed polyurethane foamed and filledbetween both the boxes; and an insulation door (not shown) whichopenably closes the front opening of the insulation box member 4.

The inside of the insulation box member 4 is vertically divided by apartition wall 5 into, for example, a refrigerating chamber 6 cooled ata refrigerating temperature (e.g., about +5° C.) above the partitionwall 5 and a freezing chamber 7 frozen at a freezing temperature (e.g.,about −20° C.) under the partition wall 5.

An indoor temperature sensor 10 for detecting a temperature in therefrigerating chamber 6 is disposed in the refrigerating chamber 6, andan indoor temperature sensor 11 for detecting a temperature in thefreezing chamber 7 is disposed in the freezing chamber 7. These indoortemperature sensors 10, 11 are connected to a controller 50 describedlater, respectively.

Moreover, a door switch for detecting opening/closing of the insulationdoor (not shown) is disposed on an inner portion of the front surface ofthe insulation box member 4. An outside air temperature sensor 12 (notshown in FIG. 2) for detecting an outside air temperature around therefrigerator 1 is disposed in the vicinity of this door switch. Theoutside air temperature sensor 12 is connected to the controller 50.

Furthermore, a mechanical chamber (not shown) is constituted in an outerlower part of the inner box 3 which is a lower part of the insulationbox member 4. The mechanical chamber contains a compressor 21constituting a part of a refrigerant circuit of a cooling device of therefrigerator 1 according to the present invention and the like.

In the cooling device of the refrigerator 1 of the present invention, asshown in FIG. 1, the refrigerant circuit is constituted of thecompressor 21, a condenser 22, a capillary tube 23 as a throttle meansand an evaporator 24. In this case, a discharge-side pipe 40 of thecompressor 21 is connected to a refrigerant pipe 22A constituting afirst condenser which is a refrigerant upstream region of the condenser22. A refrigerant pipe 22C constituting a second condenser which is arefrigerant downstream region of the condenser 22 is connected to arefrigerant pipe 42 connected to an inlet of the capillary tube 23.Moreover, a refrigerant-inlet-side pipe 45 of the evaporator 24 isconnected to an outlet of the capillary tube 23. An outlet of theevaporator 24 is connected to a suction-side pipe 41 of the compressor21 to constitute the refrigerant circuit.

Moreover, a part of the suction-side pipe 41 which connects theevaporator 24 to the compressor 21 on a suction side is disposed so thatheat exchange between the part and the capillary tube 23 is performed.In consequence, an internal heat exchanger 25 is constituted. Theinternal heat exchanger 25 is formed by arranging the capillary tube 23and the suction-side pipe 41 connected to the outlet of the evaporator24 so that the heat exchange between the tube and the pipe can beperformed. While the refrigerant flows through the internal heatexchanger 25, the refrigerant exits from the condenser 22 and enters thecapillary tube 23. The refrigerant is subjected to heat exchange betweenthe refrigerant and a refrigerant flowing through the suction-side pipe41 disposed so as to perform heat exchange, the refrigerant rejects theheat, and a pressure of the refrigerant drops. Conversely, while therefrigerant exiting from the evaporator 24 flows through thesuction-side pipe 41 of the internal heat exchanger 25, heat exchangebetween the refrigerant and the refrigerant flowing through thecapillary tube 23 is performed, and the refrigerant is heated.

Here, the condenser 22 will be described. The condenser 22 isconstituted by successively connecting the refrigerant pipe 22A (thefirst condenser) extended along a side surface of the metallic outer box2 of the insulation box member 4 and a top surface on an insulationmaterial side; a dew condensation preventive pipe 22B disposed along anopening edge 4A of the insulation box member 4; and the refrigerant pipe22C (the second condenser) disposed on a bottom surface of themechanical chamber constituted in a lowermost part of the insulation boxmember 4. While the refrigerant flows through the refrigerant pipes 22A,22B and 22C of the condenser 22, heat exchange between the refrigerantand a surrounding is performed so that the refrigerant rejects the heat.Moreover, the refrigerant pipe 22A extended along the side surface ofthe metallic outer box 2 of the insulation box member 4 and the topsurface on the insulation material side constitutes the refrigerantupstream region of the condenser 22. The dew condensation preventivepipe 22B disposed along the opening edge 4A of the insulation box member4 constitutes a refrigerant midstream region of the condenser 22. Therefrigerant pipe 22C disposed on the bottom surface of the mechanicalchamber constituted in the lowermost part of the insulation box member 4constitutes the refrigerant downstream region of the condenser 22. Thatis, the condenser 22 of the present embodiment is divided into threeflow regions including the refrigerant upstream region, the refrigerantmidstream region and the refrigerant downstream region. The refrigerantrejects the heat in the flow regions.

Moreover, the dew condensation preventive pipe 22B disposed along theopening edge 4A of the insulation box member 4 is positioned in aposition on an upstream side of the refrigerant downstream region, thatis, in the refrigerant midstream region. The dew condensation preventivepipe 22B of the present embodiment is formed of a material such ascopper or aluminum, and stored in a groove (not shown) formed betweenthe outer box 2 and the inner box 3. Furthermore, one end of the dewcondensation preventive pipe 22B is connected to the refrigerant pipe22A which is the refrigerant upstream region of the condenser 22 at alower portion of one end (A in FIG. 2) of the front surface of theinsulation box member 4. The other end of the pipe is connected to therefrigerant pipe 22C which is the refrigerant downstream region of thecondenser 22 at a lower portion of the other end (B in FIG. 2) of thefront surface of the insulation box member 4.

Specifically, as shown in FIG. 2, the dew condensation preventive pipe22B of the refrigerator 1 of the present embodiment rises upwards from aright lower end of the insulation box member 4 to a predeterminedheight, then bends at 90° in a left direction, extends in a horizontaldirection to reach a left end, turns from the left end in a U-shape, andextends to the right side along a pipe extended from the right end tothe left end. Moreover, the dew condensation preventive pipe risesupwards from the right end to a predetermined height, bends at 90° inthe left direction, extends in the horizontal direction, turns from theleft end in the U-shape, and extends along a pipe extended from theright end to the left end to extend toward the right side. Furthermore,the dew condensation preventive pipe rises upwards from the right end,extends to an upper end, and bends at 90° from the upper end toward theleft side to extend in the left direction. In addition, the pipe lowersfrom a left upper end to a lower end in a vertical direction. The pipeis extended in the groove (not shown) of the opening edge 4A in thismanner.

The controller 50 is control means for controlling the refrigerator ofthe present embodiment, and is constituted of a general-purposemicrocomputer. Moreover, the controller 50 on an input side is connectedto the indoor temperature sensors 10, 11, the outside air temperaturesensor 12 and the like. The controller on an outlet side is connected tothe compressor 21 and a fan 24F of the evaporator 24.

Moreover, the controller 50 controls an operation of the compressor 21and the number of rotations of the fan 24F of the evaporator 24 based onthe temperatures in the freezing chamber and the refrigerating chamberdetected by the indoor temperature sensors 10, 11.

It is to be noted that carbon dioxide which is a natural refrigerant isused as the refrigerant of the refrigerator 1 of the present embodiment,and the refrigerant circuit 20 on a high-pressure side is operated in asupercritical state.

Next, an operation of the refrigerator 1 of the present inventionconstituted as described above will be described with reference to theMollier diagram of FIG. 3. The controller 50 basically operates thecompressor 21 based on outputs of the indoor temperature sensors 10, 11.Especially, the controller performs ON-OFF control of the compressor 21based on the temperature in the freezing chamber 7 detected by theindoor temperature sensor 11. In consequence, the operation is performedso that the temperatures in the chambers are in a range of an upperlimit temperature set above a target temperature to a lower limittemperature set below the target temperature.

Moreover, if the temperature in the freezing chamber 7 rises in excessof the upper limit temperature of the target temperature (the targettemperature is, e.g., −20° C.), the controller 50 drives the compressor21 to start a compressing operation. In consequence, a low-temperaturelow-pressure carbon dioxide refrigerant is sucked into the compressor 21(a state A of FIG. 3), compressed by the compressor 21 to constitute ahigh-temperature high-pressure refrigerant gas, and discharged from thecompressor 21 to the refrigerant pipe 40. At this time, the carbondioxide refrigerant is compressed and brought into the supercriticalstate (a state B of FIG. 3).

The refrigerant entering the refrigerant pipe 40 and having thesupercritical state enters the refrigerant pipe 22A extended along theside surface of the metallic outer box 2 of the insulation box member 4and the top surface on the insulation material side and constituting therefrigerant upstream region of the condenser 22. While the refrigerantflows through the refrigerant pipe 22A, the refrigerant rejects theheat. At this time, in the refrigerant pipe 22A, the refrigerant rejectsthe heat while maintaining the supercritical state. In consequence,enthalpy of the refrigerant drops as much as ΔH1. That is, in therefrigerant pipe 22A, the only temperature of the refrigerant dropswithout any state change. The refrigerant is brought into a state C ofFIG. 3.

Moreover, the refrigerant which has rejected the heat in the refrigerantpipe 22A then passes through the dew condensation preventive pipe 22Bwhich is disposed along the opening edge 4A of the insulation box member4 and which is the refrigerant midstream region of the condenser 22. Inthis process, the refrigerant rejects the heat while maintaining thesupercritical state. In consequence, the enthalpy of the refrigerantdrops as much as ΔH2. Therefore, in the dew condensation preventive pipe22B, the only temperature of the refrigerant drops without any statechange, and the refrigerant is brought into a state D of FIG. 3.

The refrigerant which has rejected the heat in the dew condensationpreventive pipe 22B then passes through the refrigerant pipe 22C whichis disposed on the bottom surface of the mechanical chamber constitutedin the lowermost part of the insulation box member 4 and which is therefrigerant downstream region of the condenser 22, and the refrigerantrejects the heat. At this time, the refrigerant still maintains thesupercritical state. The enthalpy further drops as much as ΔH3 owing tothe heat rejection in the refrigerant pipe 22C. Therefore, in therefrigerant pipe 22C, the only temperature of the refrigerant dropswithout any state change, and the refrigerant is brought into a state Eof FIG. 3.

Subsequently, the refrigerant exiting from the condenser 22 enters thecapillary tube 23, and the heat exchange between the refrigerant and arefrigerant flowing through the suction-side pipe 41 is performed, thepipe being disposed so as to perform the heat exchange between the pipeand the capillary tube 23. The refrigerant is thus further cooled (theenthalpy of the refrigerant further drops as much as ΔH4). Moreover, therefrigerant expands owing to the pressure drop in the capillary tube 23,is brought into a state F of FIG. 3, and reaches the evaporator 24. Therefrigerant at the inlet of the evaporator 24 has a two-phase mixedstate in which a liquid refrigerant and a vapor refrigerant are mixed.Moreover, in the evaporator 24, the liquid-phase refrigerant evaporatesto constitute the vapor refrigerant. Ambient air is cooled by a heatabsorbing function of this refrigerant during the evaporation. Thecooled air is circulated through the chambers 6, 7 by the fan 24F (astate G of FIG. 3).

Moreover, the low-temperature low-pressure refrigerant exiting from theevaporator 24 enters the suction-side pipe 41, and passes through theinternal heat exchanger 25. In the internal heat exchanger 25, thelow-temperature low-pressure refrigerant exiting from the evaporator 24is subjected to the heat exchange between this refrigerant and therefrigerant flowing through the capillary tube 23 (the state A of FIG.3) and heated. Subsequently, the refrigerant exits from the internalheat exchanger 25, and is sucked into the compressor. This cycle isrepeated. When such an operation is repeated, the chambers 6, 7 aregradually cooled.

In addition, when the refrigerant circuit on the high-pressure side isbrought into the supercritical state as described above, the refrigerantdoes not condense in the condenser 22. Therefore, while the refrigerantmaintains the supercritical state, the refrigerant rejects the heat, andthe only temperature of the refrigerant drops.

Here, a conventional refrigerator will be described with reference toFIGS. 7 and 8. It is to be noted that in FIGS. 7 and 8, componentsdenoted with the same numerals as those of FIGS. 1 and 2 perform thesame or similar functions or produce the same or similar effects.Therefore, detailed description thereof is omitted. In a conventionalrefrigerator 100, a condenser 122 is divided into two flow regionsincluding a refrigerant upstream region and a refrigerant downstreamregion. In consideration of a refrigerant temperature rise on ahigh-pressure side during pull-down or under a high load, a dewcondensation preventive pipe 122B is disposed in the refrigerantdownstream region of the condenser 122. That is, the refrigerantupstream region of the condenser 122 is constituted by a refrigerantpipe 122A disposed along a side surface of a metallic outer box 102, atop surface on an insulation material side and a bottom surface of amechanical chamber constituted in a lowermost part, and the refrigerantdownstream region is constituted by the dew condensation preventive pipe122B of an insulation box member 4.

In the refrigerator 100 including the refrigerant circuit constituted asdescribed above, a compressor 21 is driven to perform a compressingoperation by use of a conventional refrigerant, that is, a refrigerant(e.g., a chlorofluorocarbon-based refrigerant or the like) which is notbrought into a supercritical state on a high-pressure side. In thiscase, as shown in the Mollier diagram of FIG. 9, the refrigerantcondenses in the condenser 122. Much of the refrigerant rejects heat ina two-phase region (a two-phase mixed state) of a gas and a liquid.Therefore, a refrigerant temperature in the condenser 122 hardlychanges, and the refrigerant temperature at an outlet of the dewcondensation preventive pipe 122B is a predetermined condensationtemperature which is not less than a dew point. In consequence, dewcondensation along an opening edge 4A can securely be eliminated.

However, when a carbon dioxide refrigerant or the like is used as in thepresent embodiment, the refrigerator on the high-pressure side issometimes brought into the supercritical state. In this case, since therefrigerant does not condense in the condenser 122, the temperaturedrops. In the refrigerator 100 including the conventional constitution,the refrigerant temperature at the outlet of the dew condensationpreventive pipe 122B might drop below the dew point. When therefrigerant temperature at the outlet of the dew condensation preventivepipe 122B drops below the dew point, a moisture in air around therefrigerator 1 is attached in the vicinity of the dew condensationpreventive pipe 122B, and the dew condensation is generated along theopening edge 4A.

To prevent such dew condensation, the refrigerant temperature at theoutlet of the dew condensation preventive pipe 122B needs to bemaintained at a value sufficient for preventing dew condensation alongthe opening edge 4A, that is, a dew point or more, specifically at atemperature which is about at least +4° C. higher than a temperaturearound the refrigerator 100 (e.g., in a case where the ambienttemperature is +30° C., the refrigerant temperature at the outlet of thedew condensation preventive pipe 122B needs to be maintained at +34° C.or more). However, in the refrigerator 100 having the conventionalconstitution, when the refrigerant temperature at the outlet of the dewcondensation preventive pipe 122B is set to the above temperature ormore (e.g., +34° C. or more), as shown in the Mollier diagram of FIG.10, the refrigerant temperature at an outlet of the condenser 122 rises,and the temperature cannot be lowered to a value sufficient for securinga freezing capacity of an evaporator 24. As a result, specific enthalpyof the refrigerant flowing through the evaporator 24 rises, and anenthalpy difference (q of FIG. 10) of the evaporator 24 cannotsufficiently be secured. Therefore, a problem has occurred that thefreezing capacity of the evaporator 24 remarkably deteriorates, andcooling in a refrigerating chamber 6 or a freezing chamber 7 isobstructed.

To solve such a problem, it is preferable that the dew condensationpreventive pipe 122B is disposed in a position where the refrigeranttemperature at the outlet of the dew condensation preventive pipe 122Bis not more than the dew point. However, for example, when the dewcondensation preventive pipe 122B is disposed in the refrigerantupstream region of the condenser 122, the high-temperature high-pressurerefrigerant compressed by the compressor 21 enter the dew condensationpreventive pipe 122B as it is. Therefore, the temperature along theopening edge 4A rises. When performing an operation such as opening orclosing of the refrigerator 1, a user might feel uncomfortable. Whentoughing the opening edge 4A, the user might get burnt. Furthermore,since the opening edge 4A has an excessively high temperature, there isa disadvantage that a cooling capacity of the refrigerator 100deteriorates.

To solve the problem, in the present invention, the dew condensationpreventive pipe 22B is disposed in a position on an upstream side of therefrigerant downstream region of the condenser 22. Specifically, asdescribed above, it is constituted that the condenser 22 is divided intothree flow regions including the refrigerant upstream region, therefrigerant midstream region and the refrigerant downstream region andthat the dew condensation preventive pipe 22B is disposed in therefrigerant midstream region of the condenser 22. The dew condensationpreventive pipe 22B is positioned on the upstream side of therefrigerant downstream region of the condenser 22 in this manner. Inconsequence, the temperature at the outlet of the dew condensationpreventive pipe 22B can be set to a value sufficient for preventing thedew condensation along the opening edge 4A. Furthermore, when the dewcondensation preventive pipe 22B is positioned on a downstream side ofthe refrigerant upstream region of the condenser 22, it is possible toavoid the above-described disadvantage that the refrigerant temperatureat the inlet of the dew condensation-preventive pipe 22B excessivelyrises. Furthermore, in a case where the refrigerant pipe 22Cconstituting the refrigerant downstream region of the condenser 22 isdisposed at the outlet of the dew condensation preventive pipe 22B, evenif the temperature of the refrigerant cannot sufficiently be lowered inthe dew condensation preventive pipe 22B, the refrigerant is furtherallowed to reject the heat. The temperature is sufficiently lowered, andthe refrigerant temperature at the outlet of the condenser 22 can belowered to a value sufficient for securing the freezing capacity of theevaporator 24.

That is, as compared with a case where the conventional refrigerator 100is used as shown in FIG. 3, the enthalpy difference in the evaporator 24can be enlarged. That is, the enthalpy difference of the evaporator 24is q′ larger than that in the conventional refrigerator 100 shown inFIG. 10, and the freezing capacity of the evaporator 24 can be improved.

As described above in detail, while securely preventing the dewcondensation along the opening edge 4A in the refrigerator 1 of thepresent invention, the freezing capacity of the evaporator 24 can beimproved.

Embodiment 2

It is to be noted that it has been described in Embodiment 1 that thecapillary tube 23 is used as a throttle means. However, as shown in FIG.4, an expansion valve 26 may be used as the throttle means, and an opendegree of the expansion valve 26 may be controlled by a controller 50.In this embodiment, a refrigerant pipe 42 before the expansion valve 26(on an upstream side of the expansion valve 26) and a suction-side pipe41 exiting from an evaporator 24 are arranged so as to perform heatexchange. In consequence, an internal heat exchanger 27 is constituted.A refrigerant circuit of a refrigerator of the present embodiment shownin FIG. 4 is common to Embodiment 1 described above in many respects.Therefore, detailed description of a constitution which performs thesame function as that of the refrigerator 1 of Embodiment 1 and afunction similar to that of the refrigerator or which produces the sameeffect or a similar effect is omitted.

Next, an operation of the refrigerator 1 of the present embodiment willbe described with reference to the Mollier diagram of FIG. 5. Since abasic control operation of the controller 50 is common to Embodiment 1,detailed description thereof is omitted.

Moreover, if a temperature in a freezing chamber 7 rises in excess of anupper limit temperature of a target temperature (e.g., the targettemperature is −20° C.), the controller 50 drives a compressor 21 tostart a compressing operation. In consequence, a low-temperaturelow-pressure carbon dioxide refrigerant is sucked into the compressor 21(a state A of FIG. 5), compressed by the compressor 21 to constitute ahigh-temperature high-pressure refrigerant gas, and discharged from thecompressor 21 to a refrigerant pipe 40. At this time, the carbon dioxiderefrigerant is compressed and brought into a the supercritical state (astate B of FIG. 5).

The refrigerant entering the refrigerant pipe 40 and having thesupercritical state enters a refrigerant pipe 22A extended along a sidesurface of a metallic outer box 2 of an insulation box member 4 and atop surface on an insulation material side and constituting arefrigerant upstream region of a condenser 22. While the refrigerantflows through the refrigerant pipe 22A, the refrigerant rejects heat. Atthis time, in the refrigerant pipe 22A, the refrigerant rejects the heatwhile maintaining the supercritical state. In consequence, enthalpy ofthe refrigerant drops as much as ΔH1. Therefore, in the refrigerant pipe22A, the only temperature of the refrigerant drops without any statechange. The refrigerant is brought into a state C of FIG. 5).

Moreover, the refrigerant which has rejected the heat in the refrigerantpipe 22A then passes through a dew condensation preventive pipe 22Bwhich is disposed along an opening edge 4A of the insulation box member4 and which is a refrigerant midstream region of the condenser 22. Inthis process, the refrigerant rejects the heat while maintaining thesupercritical state. In consequence, the enthalpy of the refrigerantdrops as much as ΔH2. Therefore, in the dew condensation preventive pipe22B, the only temperature of the refrigerant drops without any statechange, and the refrigerant is brought into a state D of FIG. 5.

The refrigerant which has rejected the heat in the dew condensationpreventive pipe 22B then passes through a refrigerant pipe 22C which isdisposed on a bottom surface of a mechanical chamber constituted in alowermost part of the insulation box member 4 and which is a refrigerantdownstream region of the condenser 22. Furthermore, the refrigerantrejects the heat. At this time, the refrigerant still maintains thesupercritical state. Since the refrigerant rejects the heat in therefrigerant pipe 22C, the enthalpy of the refrigerant further drops asmuch as ΔH3. Therefore, in the refrigerant pipe 22C, the refrigerantfurther rejects the heat in this process without any state change, thetemperature drops, and the refrigerant is brought into a state EI ofFIG. 5.

Moreover, the refrigerant exiting from the condenser 22 enters therefrigerant pipe 42, and passing through the internal heat exchanger 27.While the refrigerant passes through the internal heat exchanger 27, theheat exchange between the refrigerant exiting from the condenser 22 anda refrigerant flowing through a suction-side pipe 41 is performed tofurther cool the refrigerant (the enthalpy of the refrigerant furtherdrops as much as ΔH4). The refrigerant is brought into a state EII ofFIG. 5.

Subsequently, the refrigerant exiting from the internal heat exchanger27 expands owing to the pressure drop in the expansion valve 26, isbrought into a state F of FIG. 5, and reaches the evaporator 24. Here,the refrigerant has a two-phase mixed state in which a liquidrefrigerant and a vapor refrigerant are mixed. Moreover, in theevaporator 24, the liquid-phase refrigerant evaporates to constitute thevapor refrigerant. Ambient air is cooled by a heat absorbing function ofthis refrigerant during the evaporation. The cooled air is circulatedthrough the chambers 6, 7 by a fan (a state G of FIG. 5).

Moreover, the low-temperature low-pressure refrigerant exiting from theevaporator 24 enters the suction-side pipe 41, and passes through theinternal heat exchanger 27. In the internal heat exchanger 27, thelow-temperature low-pressure refrigerant exiting from the evaporator 24is subjected to the heat exchange between this refrigerant and therefrigerant flowing through the refrigerant pipe 42 and heated.Subsequently, the refrigerant exits from the internal heat exchanger 27,and is sucked into the compressor 21. This cycle is repeated. When suchan operation is repeated, the chambers 6, 7 are gradually cooled.

Even in the refrigerator of the present embodiment described above indetail, the dew condensation preventive pipe 22B is disposed in therefrigerant midstream region on the upstream side of the refrigerantdownstream region of the condenser 22 in the same manner as in the aboveembodiment. In consequence, the temperature at the outlet of the dewcondensation preventive pipe 22B can be set to a value sufficient forpreventing the dew condensation along the opening edge 4A. Furthermore,it is possible to avoid a disadvantage that the refrigerant temperatureat the inlet of the dew condensation preventive pipe 22B excessivelyrises. In addition, in a case where the refrigerant pipe 22Cconstituting the refrigerant downstream region of the condenser 22 isdisposed at the outlet of the dew condensation preventive pipe 22B, evenif the temperature of the refrigerant cannot sufficiently be lowered inthe dew condensation preventive pipe 22B, the refrigerant is furtherallowed to reject the heat. The temperature is sufficiently lowered, andthe refrigerant temperature at the outlet of the condenser 22 can belowered to a value sufficient for securing a freezing. capacity of theevaporator 24.

That is, as compared with a case where the conventional refrigerator 100is used as shown in FIG. 5, an enthalpy difference in the evaporator 24can be enlarged. That is, the enthalpy difference of the evaporator isq′ larger than that in the conventional refrigerator 100 shown in FIG.10, and the freezing capacity of the evaporator 24 can be improved. Inconsequence, while securely preventing the dew condensation along theopening edge 4A, the freezing capacity of the evaporator 24 can beimproved.

Embodiment 3

In addition, when a dew condensation preventive pipe 22B is moved from arefrigerant downstream region of a conventional condenser to an upstreamside as in the above embodiments, a usual operation is not especiallyobstructed. However, a temperature of a refrigerant flowing through thedew condensation preventive pipe 22B might rise more than necessaryduring pull-down or under a high load. That is, if the refrigeranttemperature of a refrigerant circuit on a high-pressure side abnormallyrises during the pull-down or under the high load, during heat rejectionin a refrigerant pipe 22A which is a refrigerant upstream region of acondenser 22, the refrigerant cannot sufficiently reject heat and thetemperature cannot be lowered. Therefore, a high-temperature refrigerantsometimes enters the dew condensation preventive pipe 22B. Since the dewcondensation-preventive pipe 22B is positioned along an opening edge 4Aof an insulation box member 4, a user might tough the pipe when openingor closing a refrigerator 1. If such a high-temperature refrigerantflows through the dew condensation preventive pipe 22B, a feeling ofdiscomfort might be given to the user. Moreover, the user might touchthe opening edge 4A to get burnt.

To solve the problem, a bypass pipe 28 is connected in parallel with thedew condensation preventive pipe 22B so as to extend around the dewcondensation preventive pipe 22B (one end of the bypass pipe 28, isconnected to a position A shown in FIG. 6, and the other end of thebypass pipe 28 is connected to a position B so that the bypass pipeextends around the dew condensation preventive pipe 22B). Moreover, achannel control unit is disposed which controls whether to pass therefrigerant through the dew condensation preventive pipe 22B or thebypass pipe 28. When a temperature of the dew condensation preventivepipe 22B rises more than necessary, the channel control unit executescontrol so that the refrigerant flows through the bypass pipe 28, andprevents an excess temperature rise of the dew condensation preventivepipe 22B. In the present embodiment, a three way valve 29 is disposed asthe channel control unit on an inlet side of the bypass pipe 28, thatis, the position A shown in FIG. 6. Moreover, a refrigerant temperaturesensor 13 for detecting the temperature of the refrigerant flowingthrough the dew condensation preventive pipe 22B is disposed at an inletof the dew condensation preventive pipe 22B or an outlet of therefrigerant pipe 22A of the condenser 22 which is the refrigerantupstream region of the dew condensation preventive pipe 22B. The threeway valve 29 is operated by a controller 50 based on the refrigeranttemperature detected by the refrigerant temperature sensor 13. Inconsequence, it is controlled whether to pass the refrigerant from therefrigerant pipe 22A which is the refrigerant upstream region of thecondenser 22 through the dew condensation preventive pipe 22B or thebypass pipe 28.

Specifically, the controller 50 usually controls the three way valve 29so that the refrigerant from the refrigerant pipe 22A constituting therefrigerant upstream region of the condenser 22 flows through the dewcondensation preventive pipe 22B. Moreover, when the refrigeranttemperature detected by the refrigerant temperature sensor 13 rises to apredetermined upper limit value set beforehand, the three way valve 29is switched so that the refrigerant from the refrigerant pipe 22Aconstituting the refrigerant upstream region of the condenser 22 flowsthrough the bypass pipe 28. Moreover, after elapse of a predeterminedtime, the three way valve 29 is switched so that the refrigerant fromthe refrigerant pipe 22A constituting the refrigerant upstream region ofthe condenser 22 flows through the dew condensation preventive pipe 22B.

In a case where the refrigerant temperature detected by the refrigeranttemperature sensor 13 rises to a predetermined upper limit value, whenthe refrigerant is not passed through the dew condensation preventivepipe 22B, and is passed through the bypass pipe 28, the excessivetemperature rise of the dew condensation preventive pipe 22B can beprevented. In consequence, it is possible to avoid in advance adisadvantage that owing to the excessive temperature rise of the dewcondensation preventive pipe 22B, a feeling of discomfort is given to auser or the user touches the pipe to get burnt. In addition, safety ofthe refrigerator 1 can be secured.

It is to be noted that in the present embodiment, it has been describedthat the refrigerant temperature sensor 13 for detecting the temperatureof the refrigerant flowing through the dew condensation preventive pipe22B is disposed at the inlet of the dew condensation preventive pipe 22Bor the outlet of the refrigerant pipe 22A of the condenser 22constituting the refrigerant upstream region of the dew condensationpreventive pipe 22B. A refrigerant channel is controlled so as to passthe refrigerant through the dew condensation preventive pipe 22B or thebypass pipe 28 based on the refrigerant temperature detected by therefrigerant temperature sensor 13. However, the present invention is notlimited to this embodiment. The refrigerant channel may be controlledbased on, for example, the number of rotations of a compressor 21, orthe refrigerant may be passed through the bypass pipe 28 duringpull-down of the compressor 21 or for a predetermined time.

1. A refrigerator comprising: a refrigerant circuit constituted of acompressor, a condenser, a throttle means and an evaporator and operatedon a high-pressure side in a supercritical state; and a dew condensationpreventive pipe constituting a part of the condenser and disposed alongan opening edge of an insulation box member, the condenser including atleast a first condenser and a second condenser, the dew condensationpreventive pipe being positioned between the first condenser and thesecond condenser.
 2. The refrigerator according to claim 1, furthercomprising: a bypass pipe connected in parallel with the dewcondensation preventive pipe; and a channel control unit which controlswhether to pass a refrigerant through the dew condensation preventivepipe or the bypass pipe.
 3. The refrigerator according to claim 1 or 2,wherein carbon dioxide is used as the refrigerant of the refrigerantcircuit.